"Eh, only reason I am sticking with 12 is 'cause everyone I know can handle it(its not that hard kicking..), and having 2 different calibers to do the same job makes little sense to me. Now, if I had 20's, I'd say the same thing.
I just fail to see the arguement though that a 12 kicks to hard for 10 yearolds or small women, 'cause it doesn't if you use non magnum loads. Even then, I still say anyone who can hold the gun tight against their shoulder can handle it.. Its kind of a dumb arguement when a pretty gal of 5'3 can handle magnums without a problem... and does pretty dang good with just about any other loads."
Perhaps that is the best contribution to this discussion.
There is no difference between 20g and 12g-non-magnum, it's as simple as that. However, economic reasons dictate you should use 12g.
Simple:
shotgun = 12g
all around rifle = .308/.30-06
revolver = .38sp/.357
semi-auto = 9mm
If you ignore economic reasons I'd prefer the 20g, say for a beautiful hunting gun without shooting trap etc.
Don't let ego interfer with your decisions! In fact, most people tend to take too large calibers which diminishes the fun because of higher prices and more recoil.